Project Summary Squamous cell lung cancer, a subtype of non-small cell lung cancer (NSCLC), is the second most common type of lung cancer. Also known as squamous cell carcinoma (SCC) of the lung, SCC is responsible for ~85,000 new cases of lung cancer each year and ~50,000 deaths in the United States alone. SCC is distinct from the other major subtype of NSCLC (adenocarcinoma) in terms of its histology, biomarker expression, genomic alterations, immune microenvironment and response to therapy. SCC has limited therapeutic options that are confined to chemotherapy and more recently, immunotherapy, which is only effective in a subset of patients. A major unmet need for the treatment of SCC is the identification of new therapeutic targets and treatment strategies to combat this disease. SCC has a unique histopathology and a complex microenvironment that is rich with desmoplastic stroma, keratinization and immune cells. Specifically, tumor-associated neutrophils (TANs) are enriched in mouse and human SCC, and neutrophil abundance correlates with poor prognosis and poor response to immunotherapy. Relatively little is known about how TANs impact SCC tumor progression and therapeutic response. It is notoriously difficult to model SCC in cell culture, which lacks the three-dimensional architecture of tumors, an intact immune system, and vasculature. Genetically-engineered mouse models (GEMMs) provide a complex living system that can highly recapitulate the human disease. Our laboratory pioneered the development of the first SOX2-driven SCC GEMM. We recently developed a rapid new GEMM based on alterations in Sox2/Lkb1/Nkx2-1 (SNL) where SCC tumors highly resemble the human disease in terms of histopathology, genetics, and immune microenvironment. This new SNL model represents a unique immune- competent tool to investigate how TANs shape tumor progression and therapeutic response. The objective of this study is to elucidate the role of TANs in squamous lung cancer development, progression and response to therapy. We hypothesize that TANs promote squamous cell fate by increasing reactive oxygen species (ROS), which are implicated in tumor transdifferentiation, and by promoting neutrophil extracellular traps (NETosis). To test these hypotheses, we will: 1) Determine the mechanism by which TANs alter tumor cell fate. 2) Determine whether TANs promote squamous lung cancer progression via ROS and/or NETosis. 3) Determine whether neutrophil depletion enhances response to chemotherapy and/or immunotherapy. This approach is innovative because we will employ: 1) our novel immune-competent SCC GEMM that recapitulates key features of the human disease, 2) neutrophil depletion strategies that are in clinical trials, and 3) state-of-the-art technologies including single cell RNA-sequencing and natural cancer-associated inhibitors of NETosis. This research is significant because TAN function in SCC is almost completely unexplored and TANs may represent a new therapeutic target for this intractable disease.